The invention relates to a semiconductor diode and production method suitable therefor.
It is known that in the course of hard commutation of diodes, current chopping can occur in the diode. The consequence of such current chopping is that severe voltage or current oscillations occur. If such oscillations exceed maximum values that are permissible for the diode, then the diode may be destroyed. Destruction of the diode may also be caused by excessively severe interference effects on driving processes that are brought about by the current or voltage fluctuations, and resultant incorrect behavior of the driving processes. The problem area described above occurs particularly in the case of circuits with high leakage inductance, high currents (for example in the case of power semiconductors being connected in parallel in solid fashion) and in the case of high voltages with respect to which the diode is commutated.
A first possibility for preventing current chopping consists in reducing the current gradient in the course of the commutation of the diode. However, this leads to an increase in switch-on losses of the associated switch and is therefore undesirable.
A second possibility for preventing current chopping emerges from the following considerations: in order to build up a reverse voltage at the terminals of a diode, for example a pn−n diode, it is necessary to deplete a flooding charge (beginning at the pn junction). Since increasing the reverse voltage by ΔU is necessarily associated with the depletion of a charge packet ΔQ of the flooding charge, it is not possible, as long as sufficient flooding charge is present, for a diode reverse current to undergo chopping and for the reverse voltage to rise abruptly. Consequently, if sufficient flooding charge is present behind the end of the space charge zone at the end of a switching operation in the diode, current chopping can be prevented (the flooding charge diffuses apart and thereby still maintains a certain current flow). The presence of flooding charge furthermore has the effect that when a maximum reverse voltage is present, the diode reverse current does not immediately undergo chopping, whereby it is possible to avoid high current changes on account of the parasitic inductances always present and resultant voltage spikes at the diode. By increasing the diode thickness, equally there is also more flooding charge available for avoiding current chopping. What is disadvantageous about increasing the diode thickness, however, is that both the forward losses and the switching losses of the diode are increased.
The object on which the invention is based is to specify a semiconductor diode and a production method suitable therefor by means of which the disadvantages described above can be avoided.